If you want to run tires larger than 30.5", you either need to install 1.5" wheel spacers, or obtain a wheel with a backspacing of less than ~5" (a stock wheel has 6" of backspacing and 7" rim width) AND a lift (either suspension or body will work). Depending on your particular combination, it may require some trimming of the inner wheel well.

Measuring the rim backspacing:

A set of 4 wheel spacers:

If you wish, a wheel spacer can also act as an adapter to change the lug pattern to match a new wheel. When the spacer also changes the bolt pattern, it is commonly referred to as a Wheel Adapter. If you are planning to use the stock bolt pattern, remember, our stock lug pattern is 6x5", or 6x127mm. It is NOT 6x5.5", as most Chevy trucks are.

A common question comes up regarding the hubcentric and wheelcentric terms. Hubcentric means the inner bore of the wheel spacer matches the vehicle hub outer diameter. Wheelcentric means that the spacer has a small lip protruding from it's wheel face. This lip's outer diameter matches the wheel's inner hub bore. The purpose of matching these bores is to decrease the concentric offset between the components. It unloads the wheel studs during the torquing process, which allows the wheels to theoretically have less vibration at speed. Some people say it's unnecessary... to each their own.

The centerbore is also critical. OEM and many aftermarket wheels use a 78.3mm centerbore, but getting custom adapters or spacers machined with this dimension will end up being hard or impossible to fit, or sticky to change on the trail without kicking the tire off from the inside. Your machinist should add 2-3 thousandths to the hubcentric centerbore opening to fit the vehicle, and reduce the diameter of the wheelcentric lip on the outside to ensure a good fit to the wheel.

As always, if you're going to fit aftermarket wheels, it's best to acquire the wheels FIRST, then measure the centerbore EXACTLY, then order your spacers or adapters to fit. Slows down the process but makes sure you don't have to remachine them yourself. You can guess how I figured this out.

Okay, got my spacers from Fred. He's now including a warning about factory studs protruding past the spacers but, not other instructions. What should these be torqued to? Should I use thread lock? How often should I re-check the torque?

signguy62 wrote:Okay, got my spacers from Fred. He's now including a warning about factory studs protruding past the spacers but, not other instructions. What should these be torqued to? Should I use thread lock? How often should I re-check the torque?

Thought this could be helpful just in case someone was looking at using the stock 18" wheels with spacers and oversized tires. I know I was at one time, but I like the American Racing Fuel 17x8 wheels in our bolt pattern, which seem to have the perfect backspacing + offset for oversized tires and I can get them at a decent price. The info on stock 17" wheels wouldn't quite match up...

Thought I'd share for the sake of completeness of info here. I'm sure we won't get many Denali/SS owners on 18's looking for off-road wheel/tire info, but there it is.

(Feel free to add the info to the OP and delete this post if you feel it's useful enough.)

Philberto wrote:Full Disclosure: I have the ebay spacers, so they aren't wheelcentric...

Im debating on whether or not to purchase the spacers on Ebay. $130 is a lot lets that $365, but i dont want to purchase a bad product. JD mentioned non wheel centric might vibrate at higher speeds. Anybody got a few words of input?

Save your money, and get a set of wheel spacers from FRED. he can make them hub and wheel centric for ya. He costs a bit more, but you get a much much better product, and peace of mind. Remeber, things that sell cheap do so for a reason. Probably made out of crapy materials, or made by someone who doesnt have much experience ect...

Gonna disagree with Zero here as well. 20k miles, maybe 2k of them offroad, and I've inspected the spacers. Properly torqued, no stretching or deformation of the studs, and have had no vibrations on them at all. If you're that concerned, just have them balance the wheels on the car, but I've had no problems.

This has been an on going topic of beliefs and miss information. Fred makes a very high quality product, one you would never have issue with. His spacers are not cheap and he 'must stick to his guns' on his pricing. You will not be failed by Fred, his products or the constant drone of The Roadie.That being said, there have been no issues with the other spacers when installed properly.

Wow, I love this site and the members...Quick responses! To be honest I think I'm gonna go with the ebay ones. I'm gonna do a little more research, but from what I can sum up, as long as they are set up properly and consistantly torqued, I feel that there shouldn't be any problems. Thanks

X3, or 4. I am on my second set of spacers from the vendor that Mark deals with. These thing are great! Not to mention that the maker started producing them in the 1.5" thickness so we don't have to worry about grinding studs down anymore.

No longer a 360 owner, but you can't get rid of me "stranger in a strange land"TB BUILD

That kind of slander is uncalled for. There are plenty of people that are wheeling the "ebay adapters" and have had no trouble with them! In fact the only trouble I have seen reported with them was due to improper mounting when they were being run at 1.3". That is not an issue now that they are being run at 1.5". Save yourself $200 and order the adapters from MarkMC. You will not be disappointed!

Twenty years from now you will be more disappointed by the things that you didn’t do than by the ones you did do. So throw off the bowlines. Sail away from the safe harbor. Catch the trade winds in your sails. Explore. Dream. Discover.- Mark Twain--Build--

That kind of slander is uncalled for. There are plenty of people that are wheeling the "ebay adapters" and have had no trouble with them! In fact the only trouble I have seen reported with them was due to improper mounting when they were being run at 1.3". That is not an issue now that they are being run at 1.5". Save yourself $200 and order the adapters from MarkMC. You will not be disappointed!

I didn't realize Mark was selling spacers now also. Guess I'd better read more threads before commenting on this issue again.

Easy bro, its not slander. Its a fact of life. 99% of the time, cheap stuff is cheap for a reason. And you can justify the high cost of the other product at times due to manufacturing process ect.

How often have you guys bought something from pepboys and it was a piece of crap, but then you buy lets say your lights right from hella or another outstanding company...the price is about triple, but the product is 100x better...... so you see the point i am trying to make here.....at times, you get what you pay for.

Also, this guy asked for everyones opinion...I gave mine....if you dont like it...fine...thats your opinion. I dont need to sit here and let people talk about my post as if I am some moron. We all have our theories about what is best for each of our trucks. personally, I //// hate ebay. Most of the sellers on there are crooks, and most of the crap on there is just that...simply crap. i prefer to buy my parts brand new, right from the manf. for piece of mind.

My mentor taught me a great saying.....millions and millions of dollars are spent designing vehicles.....you are not gona improve a design over night in your garage....it just doesnt happen that way.....there is extensive testing, planning, that parts go through.

That reason is exactly why I buy Bartons armor. It is tried, and treu, tested to the bone. Even computer simulations are done first, before product is made to ensure quality.

Let's not pile on Zero. I merely said I disagreed with him, not that he was slandering. I think the main thing that keeps the other spacers cheaper is the sheer volume these guys make and the lack of a wheelcentric lip on the edge of them. But it is very good to encourage everybody to do their research and not assume that cheaper is always a good thing.

For instance, I did have a Harbor Freight axe, brand new, that didn't survive the Big Bear Trip. Handle split clean in half. I didn't know you could mess up something that simple.

Mark has teamed up with the ebay wheeladapters seller, and is now offering their product as well.

Zero wrote:Easy bro, its not slander. Its a fact of life. 99% of the time, cheap stuff is cheap for a reason. And you can justify the high cost of the other product at times due to manufacturing process ect.

How often have you guys bought something from pepboys and it was a piece of crap, but then you buy lets say your lights right from hella or another outstanding company...the price is about triple, but the product is 100x better...... so you see the point i am trying to make here.....at times, you get what you pay for.

Sorry Zero, I wasn't trying to be an ass. I understand the "get what you pay for" concept. Yes you can compare Hella lights versus the pep boys special. However the question was about this particular product. There are hundreds of Trailvoy members that are running these and have had no issues what so ever. There is no reason for him not to save some money and go with this product.

Twenty years from now you will be more disappointed by the things that you didn’t do than by the ones you did do. So throw off the bowlines. Sail away from the safe harbor. Catch the trade winds in your sails. Explore. Dream. Discover.- Mark Twain--Build--